Physics  electrons, waves and photons
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Ampere
A current or rate of flow of charge of one coulomb per second

Charge
A fundamental property of matter and may be positive or negative

Coulomb
A unit of charge produced when a current of 1A flows for 1s

Kilowatt hour
A unit of energy produced when a device rated at a power of 1kW is used for 1 hour (equal to 3.6 MJ)

Kirchhoff's 1st Law
The sum of currents entering a junction is equal to the sum of currents leaving a junction (conservation of charge)

Kirchhoff's 2nd Law
The sum of emf around a loop is equal to the sum pd round the loop (conservation of energy)

Mean drift velocity
The average velocity that a charged particle attains due to an electric field

Terminal pd
The voltage across the ends of a battery and is equal to the emflost volts

Ohm
The resistance of a conductor through which a current of 1A is flowing when the pd across it is 1v

Ohm's Law
The current though a metallic conductor is directly proportional to the potential difference across it provided there is no change in the physical conditions (eg temperature) of the conductor

The resistance of an LDR
As light intensity increases, resistance of the LDR decreases

Photon
A quantum of energy of electromagnetic radiation (E=hf)

Resistivity
(Resistance x cross sectional area) / length


Resistance
Pd across conductor / current across conductor

Potential difference (pd)
Between two points in a circuit is the amount of energy in joules changed into other forms per coulomb of charge that passes from one point to another

Power
Rate of conversion of energy in watts (= joules per second)

Volt
One joule of energy per coulomb of charge

Work function
The minimum photon energy needed to eject a photoelectron from a metal

Current
The rate of flow of charge

EMF
Electrical energy transferred per unit charge as the charge passes through a source

Internal resistance
Is responsible for energy lost in a cell when a current flows though it

Threshold frequency
The minimum frequency of incident radiation needed to release photoelectrons

Coherence
Constant phase difference

Laws of reflection
 1. The reflected ray, the incident ray and the normal are coplanar
 2. The angle of reflection is equal to the angle of incidence

Malus' Law
I =


UV  B
Causes sunburn and skin cancer

Wavelength of visible light
 m
 m

Intensity
 Intensity = power / surface area
 Intensity amplitude^{2}^{}

For a maximum the path difference...
Is equal to a whole number of wavelengths^{}

For a minimum the path difference...
Is equal to an odd number of half wavelengths

Transverse wave
The direction of particle oscillation is perpendicular to the direction of energy travel

Longitudinal wave
The direction of particle oscillation is parallel to the direction of energy travel

Wavelength
The distance between two consecutive points which are in step

Displacement
How far and in which direction each particle is from it's central undisturbed position

Amplitude
The maximum displacement that the particles obtain from their central undisturbed position

Frequency
The number of complete cycles of oscillation performed per second

Period
The time taken to perform one complete cycle of oscillation

Relationship between frequency and period
f = 1/T

Wave speed
V = f

In phase
Two waves are said to be exactly in phase if all the crests of one exactly align with the crests of the other

Out of phase (180•)
If the crests of one wave line up with the troughs of another

Polarisation
A property of transverse waves where all the oscillations are in the same plane

Pitch
Of a sound depends on frequency

Loudness
Of sound is determined by the amplitude of the vibrations

The principle of superposition
The vector addition of the displacements of two or more waves that meet